1. Field of the Invention
The invention relates to an apparatus and method of mail sorting.
2. Description of the Prior Art
In modern mail sorting offices each item of mail passes through two separate processing stages. In the first stage, address information is extracted from the mail items and corresponding address or sorting barcodes are printed on each item. In the second stage, the mail items are sorted using automatic sorting machines into a predetermined sorting sequence.
Both stages are time consuming and expensive in terms of the resources required. For instance, the second stage requires large numbers of mail sorting machines each having a large number of sorting bins. Due to the cost of manual sorting, the tendency is to increase the number of sorting tasks for which automatic sorting machines are used.
However, automatic mail sorting machines are themselves very expensive and therefore it is of paramount importance that the most efficient use possible be made of them.
Nowadays, computers are generally used to control and optimize the sorting process in order to reduce the number of bins required in the sorting machines and the number of times each mail item or a batch of mail items being sorted must pass though a sorting machine.
For example, it is possible to reduce the sorting time required by sorting the mail items into a delivery sequence defined by the destination addresses as follows. Consider an imaginary village having 1000 possible addresses in which, on any given day, an average of 100 pieces of mail need to delivered to 100 different ones of these addresses and a sorter is available which has 10 pockets. If sorting is performed according to address number then the mail will have to be passed through the sorter 3 times (equal to log.sub.10 1000), If, on the other hand, each mail item is assigned, via suitable processing of address information extracted from the item, a sequence number and the mail is sorted according to the sequence numbers only 2 passes are required (equal to log.sub.10 100).
However, in order to implement this method it is necessary to know the correct mail sequencing and for all the mail items to be sorted to be physically present at the sorting location before the start of the sorting process. In practice, since the mail will be arriving at the sorting location from a number of different places, it will not normally all arrive at the same time. Therefore, the need to wait until it has all arrived before starting the sort process creates a bottleneck in the process which leads to a delay.